The present invention generally relates to a high frequency heating arrangement and more particularly, to a heat generating vessel or container for use in a microwave oven which is one example of high frequency heating apparatuses, so as to generate heat through projection of microwaves irradiated from a magnetron (i.e., a high frequency generating means) for heating an object to be cooked, and also for baking thereof.
A microwave oven is a cooking apparatus arranged to guide microwaves emitted from a magnetron into an oven interior or heating chamber for irradiation onto an object to be cooked so as to effect cooking by causing said object itself to generate heat.
However, there are some items to be cooked which are not suitable for direct heating by microwaves such as those requiring scorched portions or those to be subjected to cooking after expediting fermentation by raising temperature thereof.
In order to deal with the cooking items as referred to above, there has been proposed a microwave oven further provided with a sheathed heater in the heating chamber so as to make it possible to subject the item to be cooked to heat treatment through utilization of heat irradiated from said sheathed heater besides the microwave radiation.
In the microwave oven of the above described type, however, since two kinds of heating means, i.e., the magnetron and the sheathed heater, must be provided as heat sources, not only do cost increase, but the construction of the microwave oven is undesirably complicated, with a consequent increase in the size of the apparatus on the whole.
Therefore, in order to overcome the various problems as described above, there has been recently developed a heat generating member composed of a plate in a double layer construction formed by laminating a heat generating substance (e.g., silicon carbide, ferrite or the like) which generates heat through irradiation of microwaves and an inorganic heat insulating base material (e.g., glass, ceramic or the like). There has also been proposed a heat generating member made of a silicon carbide group ceramic molded plate.
The microwave oven employing the heat generating members of the above described type is capable of effecting both the dielectric heating and the heating by heat radiation, only through irradiation of microwaves and is referred to as a multi-function microwave oven.
Incidentally, due to the fact that a so-called "home bakery" or household bread baking unit has recently become a popular article, a microwave oven provided with a bread baking function has been studied and manufactured as an actual commercially available product.
Although a bread baking container or hopper (referred to as a hopper hereinafter) to be disposed in the oven interior or heating chamber of the microwave oven is generally arranged to be heated indirectly, this practice requires parts for subjecting heated air to convection for efficient conduction of heat to the hopper, and thus, not only do cost increase, but power consumption is undesirably raised due to poor heating efficiency, even when the heat is conducted in an efficient manner.
On the other hand, as a direct heating practice, there has conventionally been proposed an arrangement in which a microwave absorbing heat generating material is applied over an outer surface of a hopper as disclosed in Japanese Patent Laid-open Publication Tokkaisho No. 58-52916, or another arrangement in which a microwave absorbing heat generating material is coated on a ceramic or glass container as disclosed in Japanese Patent Laid-open Publication Tokkaisho No. 58-52917.
However, the known arrangements as described above have such problems that uneven baking (or scorching) may take place or yeast for fermentation is undesirably killed if applied to the bread bakery, since microwaves are transmitted into the container. Due to uneven microwave distribution within the heating chamber, the temperature for heating the container is not uniform, thus resulting in irregular baking (i.e. scorching) of the bread.
Another disadvantage inherent in the conventional arrangement is such that, if the main container and the lid are made of metal, electric discharge takes place at the junction therebetween for undesirable fusing.
Meanwhile, in the conventional heating container for baking, for example, adapted to bake bread in a rectangular or square shape (so-called Pullman shape), an exclusive lid is provided for closing an upper opening of the heating container. In the kneading process and fermentation process for the manufacture of bread, the lid is removed for the processing, while during baking, the lid is mounted on the heating container to obtain the bread in the required shape.
However, in the known heating container for baking of the above described type, the baked bread is sliced through eye measurement, since it is provided with no marks or the like for slicing the square bread in uniform thickness, and thus, the thickness tends to differ from slice to slice.